Span interface should only allow LinkedTo at creation.

[VineethReddy02]

I have removed AddLink and Link from the Span interface and all it references, replaced AddLink with addlink, Also Removed respective unit tests for AddLink & Link.
#329

This is my first PR to open-telemetry. Feel free to request changes or let me know if I need to catch up with some pre-requisites. :)

[paivagustavo]

Hey @VineethReddy02, thanks for taking some time and sending this PR.

Changes looks good just a couple of notes.

[jmacd]

I wasn't following this PR and the associated issue closely, my apologies. I see there is still a spec for AddLink in the spec, it reads:

- An API to record a single `Link` where the `Link` properties are passed as
  arguments. This MAY be called `AddLink`.
- An API to record a single `Link` whose attributes or attribute values are
  lazily constructed, with the intention of avoiding unnecessary work if a link
  is unused. If the language supports overloads then this SHOULD be called
  `AddLink` otherwise `AddLazyLink` MAY be considered. In some languages, it might
  be easier to defer `Link` or attribute creation entirely by providing a wrapping
  class or function that returns a `Link` or formatted attributes. When providing
  a wrapping class or function it SHOULD be named `LinkFormatter`.

[paivagustavo]

@jmacd It is also stated at the specs that you quoted that:

During the Span creation user MUST have the ability to record links to other Spans.

And there is no specification of an AddLink as an operation of a Span. We can compare to the Attributes that are specified in both "Span Creation" and on the "Span Operations".

I've also double-checked the java implementation and there is no method like that there.

[jmacd]

OK. I can see that interpretation is sensible. If @rghetia signs off, this is good to go.

[rghetia]

you need to add the links with StartSpan as below

	span := startSpan(tp, "Links",
		apitrace.LinkedTo(sc1, key.New("key1").String("value1")),
		apitrace.LinkedTo(sc1,
			key.New("key2").String("value2"),
			key.New("key3").String("value3"),
		),
	)

and then check for non-nil links

[rghetia]

same thing here.

[rghetia]

OK. I can see that interpretation is sensible. If @rghetia signs off, this is good to go.

I am fine with this PR.

[iredelmeier]

LGTM once @rghetia and @paivagustavo's test requests are made. If it would help, I'm happy to jump on Zoom to pair on the changes.

[VineethReddy02]

I made all the requested changes. But squashed all the previous commits into one commit due to some signing issue.

Thanks for all the guidance.

[paivagustavo]

Awesome @VineethReddy02!

Small change request but it looks good to me.

[paivagustavo]

These two LinkedTo are not being used, just remove them.

[VineethReddy02]

Sorry, Got it. I already put them in startSpan() function.

[paivagustavo]

Same as above, just delete this.

[rghetia]

@iredelmeier can you please remove the block if you are okay with the latest changes?